[crac] RFR: 8374491: CPUFeatures: check performance regression of AVX_Fast_Unaligned_Load

[Jan Kratochvil]

A regression by [JDK-8372863](https://bugs.openjdk.org/browse/JDK-8372863).

On AWS m1.small:

bin/java -XX:+ShowCPUFeatures --version
This machine's CPU features are: -XX:CPUFeatures=0x142000070bbdf,0x380
CPU features being used are: -XX:CPUFeatures=0x142000070bbdf,0x380
Re-exec of java with new environment variable: GLIBC_TUNABLES=:glibc.cpu.hwcaps=,-AVX_Fast_Unaligned_Load
This machine's CPU features are: -XX:CPUFeatures=0x142000070bbdf,0x380
CPU features being used are: -XX:CPUFeatures=0x142000070bbdf,0x380
openjdk 25-internal 2025-09-16
OpenJDK Runtime Environment (fastdebug build 25-internal-adhoc.azul.crac-git)
OpenJDK 64-Bit Server VM (fastdebug build 25-internal-adhoc.azul.crac-git, mixed mode, sharing)

That is a needless re-exec.

-------------

Commit messages:
 - ZULU-84726: CPUFeatures: check performance regression of AVX_Fast_Unaligned_Load

Changes: https://git.openjdk.org/crac/pull/283/files
  Webrev: https://webrevs.openjdk.org/?repo=crac&pr=283&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8374491
  Stats: 5 lines in 1 file changed: 2 ins; 2 del; 1 mod
  Patch: https://git.openjdk.org/crac/pull/283.diff
  Fetch: git fetch https://git.openjdk.org/crac.git pull/283/head:pull/283

PR: https://git.openjdk.org/crac/pull/283